1. Technical Field
The present invention relates generally to digital signal processing.
2. Background and Relevant Art
Digital communication and signal processing have become ubiquitous in the modern world. In particular, over-the-air communication via cellular phones, Wi-Fi connections, and other similar communication devices has experienced an explosion in bandwidth requirements and usage in recent years. This increase in bandwidth utilization has resulted in significant innovations within the area of communication technologies.
A variety of different methods are used to optimize bandwidth within particular frequency bands. For example, cross-polarization of signals can be used to effectively double the bandwidth of a particular frequency channel. Cross-polarized signals can be transmitted within the same frequency band, but at distinguishably different polarizations. A receiver can receive both signals within the same frequency band and filter the signals from each based upon the difference in polarization. For instance, a first signal may be transmitted at a vertical polarization and a second signal transmitted at a horizontal polarization. The receiver can separate the signal data in the vertical polarization from the signal data in the horizontal polarization. As such, the receiver can simultaneously receive two different signals within a single frequency band.
One of skill in the art will recognize that while cross-polarization can provide significant benefits for transmitted signals, potential drawbacks can also arise. For example, cross-channel interference between cross-polarized signals can corrupt the data in each respective signal. Co-channel interference arises when signal information at a particular polarization (e.g., the vertical polarization) is smeared into the signal information within another polarization (e.g., the horizontal polarization). If the co -channel interference is significant enough, data loss from one or both of the signals can occur.
To address co-channel interference, various methods of cross-polarization interference cancellation (“CPIC”) are used within conventional digital signal processing systems. Fortunately for CPIC, in many cases, the cross-polarized signals are broadcasted from the same source, which can aid in syncing the respective signal rates. In particular, conventional cross-polarization signals are broadcast at the same symbol and/or chipping rates. The common symbol and/or chipping rate is crucial within the conventional art for properly retrieving the respective data signals.
In addition to co-channel interference caused by cross-polarized signals, co -channel interference can also arise in other signal processing contexts. For example, a digital signal processing system with directional antennas that are receiving different signals from different directions, but within the same frequency band, can also experience co-channel interference. Similar to cross-polarization interference, the directional signals can interfere with each other and introduce interference to the data of interest.
Several methods are known in the art for removing co-channel interference from signals of interest. Conventional systems, however, rely upon the underlying signal having equal symbol and/or chipping rates in order to isolate and remove the co -channel interference. Accordingly, there are a number of problems within the art relating to processing signals with co-channel interference, when the underlying signals comprise different symbol and/or chipping rates.